Titration Of Phosphoric Acid With Naoh

Titration of Phosphoric Acid with NaOH: A Step-by-Step Guide

Titration is a crucial technique in chemistry used to determine the concentration of an unknown solution by reacting it with a solution of known concentration. This article focuses on the titration of phosphoric acid (H₃PO₄), a weak triprotic acid, with sodium hydroxide (NaOH), a strong base. Understanding this specific titration is fundamental to grasping acid-base chemistry and its applications in various fields, from environmental monitoring to food science.

1. Understanding Phosphoric Acid and its Behavior

Phosphoric acid is a weak acid, meaning it doesn't fully dissociate (break apart into ions) in water. This is unlike strong acids like hydrochloric acid (HCl) which completely ionize. The key to understanding its titration lies in its triprotic nature. This means it can donate three protons (H⁺ ions) in three distinct steps:

Step 1: H₃PO₄ + H₂O ⇌ H₂PO₄⁻ + H₃O⁺
Step 2: H₂PO₄⁻ + H₂O ⇌ HPO₄²⁻ + H₃O⁺
Step 3: HPO₄²⁻ + H₂O ⇌ PO₄³⁻ + H₃O⁺

Each step has its own equilibrium constant (Ka), indicating the extent of dissociation at each stage. Ka1 > Ka2 > Ka3, meaning the first proton is easiest to donate, followed by the second, and then the third. This stepwise dissociation leads to multiple equivalence points during the titration.

2. The Titration Process: A Step-by-Step Approach

The titration involves slowly adding a standardized NaOH solution (a solution with precisely known concentration) to a known volume of phosphoric acid solution of unknown concentration using a burette. A pH meter or an indicator (like phenolphthalein) is used to monitor the pH change during the addition of NaOH.

Steps:

1. Preparation: A precise volume of phosphoric acid is measured into a flask. A few drops of an appropriate indicator (phenolphthalein for visualization or a pH meter for precise measurement) are added.
2. Titration: NaOH solution is slowly added from the burette while constantly swirling the flask. The pH changes gradually at first, then rapidly near the equivalence points.
3. Equivalence Points: There are three equivalence points corresponding to the three dissociation steps of phosphoric acid. These are marked by significant pH jumps. The first equivalence point represents the neutralization of the first proton, the second the second proton, and so on.
4. Data Analysis: The volume of NaOH used to reach each equivalence point is recorded. Using stoichiometry (the relationship between reactants and products in a chemical reaction), the concentration of the original phosphoric acid solution can be calculated.

3. Practical Example and Calculations

Let's say we titrated 25.00 mL of phosphoric acid with 0.100 M NaOH. We observe the first equivalence point at 12.50 mL of NaOH added. Using the balanced equation for the first step:

H₃PO₄ + NaOH → NaH₂PO₄ + H₂O

Moles of NaOH used = (0.100 mol/L) (0.01250 L) = 0.00125 mol

Since the mole ratio of H₃PO₄ to NaOH is 1:1 in the first step, the moles of H₃PO₄ are also 0.00125 mol.

Concentration of H₃PO₄ = (0.00125 mol) / (0.02500 L) = 0.0500 M

This calculation provides the concentration based on the first equivalence point. Similar calculations can be performed for the second and third equivalence points, but the stoichiometry will change accordingly.

4. Titration Curves and their Significance

Plotting the pH against the volume of NaOH added creates a titration curve. The curve for phosphoric acid titration shows three distinct regions of rapid pH change, corresponding to the three equivalence points. The curve also reveals the pKa values of phosphoric acid, representing the acidity strength at each dissociation step.

5. Applications and Importance

Phosphoric acid titration has widespread applications in various fields:

Food industry: Determining the concentration of phosphoric acid in beverages and food additives.
Environmental monitoring: Analyzing water samples for phosphate levels, an indicator of pollution.
Agricultural chemistry: Determining the phosphate content in fertilizers.
Pharmaceutical industry: Quality control of pharmaceutical products containing phosphoric acid.

Key Insights & Takeaways

Understanding the stepwise dissociation of phosphoric acid is crucial for interpreting the titration curve and accurately determining its concentration. The titration technique offers a precise and reliable method for quantifying acids and bases.

FAQs

1. Why are there three equivalence points in the titration of phosphoric acid? Because phosphoric acid is a triprotic acid, it can donate three protons, resulting in three neutralization steps and thus three equivalence points.

2. What indicators are suitable for this titration? Phenolphthalein is suitable for observing the second equivalence point visually, while a pH meter provides more accurate determination of all three equivalence points.

3. How does the temperature affect the titration? Temperature affects the equilibrium constants (Ka values), influencing the pH at each equivalence point. Consistent temperature is essential for accurate results.

4. What if I don't have a standardized NaOH solution? You'll need to standardize the NaOH solution first using a primary standard (a substance of known high purity), such as potassium hydrogen phthalate (KHP).

5. Can I use this method for other polyprotic acids? Yes, the same principles apply to titrating other polyprotic acids, but the number of equivalence points and the calculations will depend on the number of acidic protons the acid possesses.

Search Results:

Titration of H3PO4 with NaOH - Chemistry Stack Exchange 5 Sep 2015 · Find the equivalents of $\ce{H^+}$ from phosphoric acid (a) and the equivalents of $\ce{OH^-}$ from $\ce{NaOH}$ (b). Also calculate the total volume. Number of equivalents=$NV$.

Determination of phosphoric acid with sodium hydroxide This Application Note presents an acid-base titration where the concentration of phosphoric acid is determined over all three of its dissociable protons by titrating it with sodium hydroxide. www.metrohm.com 1

Titration of Phosphoric Acid and Buffers - Rice University To determine the amount of acid in an unknown sample, you will need to add a known amount of base until the acid and base are neutralizes. This technique is known as titration, and it is widely used in chemistry and other natural sciences.

Experiment Ka1 OF PHOSPHORIC ACID BY TITRATION • experience the titration of a triprotic acid. • learn proper technique in pipette and buret usage. • determine the first dissociation constant for phosphoric acid from the titration curve. • become familiar with Pauling’s rules for oxyacid strength. INTRODUCTION: Pho spho ric acid, H 34

7.4: Solving Titration Problems - Chemistry LibreTexts A titration of the triprotic acid $H_3PO_4$ with $NaOH$ is illustrated in Figure $\PageIndex{2}$ and shows two well-defined steps: the first midpoint corresponds to $pK_a$1, and the second midpoint corresponds to $pK_a$ 2.

Calculate Ph In Titration: Unlock The Formula For Accurate … 30 Dec 2024 · Let’s consider a weak acid-strong base titration of acetic acid (CH₃COOH) with sodium hydroxide (NaOH). Given: - Initial concentration of acetic acid: 0.1 M - Volume of acetic acid: 50 mL - Volume of NaOH added: 25 mL - pKa of acetic acid: 4.76. Solution: Calculate the moles of acetic acid: 0.1 M × 0.050 L = 0.005 moles

pH and titration - umb.edu In this experiment you will titrate H3PO4 with a dilute solution of NaOH. H3PO4 is phosphoric acid. It is the major acid that gives cola its acidity. It is a triprotic weak acid, which means contains three acidic protons. Therefore, it has three acid dissociation constants; Ka1 = 7.11⋅10-3, Ka2 = 6.34⋅10-8 and Ka3 = 8⋅10-13.

Titration of a Polyprotic Weak Acid with Sodium Hydroxide 29 Aug 2023 · The concentration of citric or phosphoric acid can be determined through a titration with sodium hydroxide, provided you realize which equivalence points can be successfully monitored during the titration.

Phosphorus Acid Titration | PDF | Titration | Chemistry - Scribd The document describes two experimental methods to determine the concentration of a phosphoric acid solution: 1) Titration using a pH indicator. A 10.0 mL aliquot is titrated with 0.1M NaOH until the color changes from yellow to blue at pH 4.7. 2) Titration using a pH meter.

Titration of phosphoric acid with sodium hydroxide 13 Nov 2024 · Titration of the phosphoric acid H 3 PO 4 is an interesting case. Although often listed together with strong mineral acids (hydrochloric, nitric and sulfuric) phosphoric acid is relatively weak, with pK a1 =2.15, pK a2 =7.20 and pK a3 =12.35.

Potentiometric Titration of Polyprotic Acid and Base Titration of Phosphoric Acid With your volumetric pipet, measure 25.00 mL of 0.06 M (nominal) phosphoric acid into a 100 mL beaker and complete the set-up in Figure 1 to titrate with standardized 0.2 M NaOH.

CHM 106 Potentiometric Titration of Phosphoric Acid In this lab, we will conduct a potentiometric titration of a solution of phosphoric acid (H3PO4) of unknown concentration. We will determine the concentration of the phosphoric acid solution and the values for the first two acid dissociation constants. We will also examine indicator selection in …

Determination of phosphoric acid with sodium hydroxide The H 3 PO 4 (acid solution) reacts with NaOH (strong base) via the following neutralization reaction mechanism: H 3 PO 4 + 3 NaOH → Na 3 PO 4 + 3 H 2 O. An appropriate amount of sample is pipetted into the titration beaker and then deionized water and …

Lab6 - lab report - CHM 106 Potentiometric Titration of Phosphoric Acid ... In this lab, we will conduct a potentiometric titration of a solution of phosphoric acid (H 3 PO 4 ) of unknown concentration. We will determine the concentration of the phosphoric acid solution and the values for the first two acid dissociation constants.

How to carry out an acid-alkali titration. - BBC Bitesize A titration is a practical technique in which an acid close acid Corrosive substance which has a pH lower than 7. Acidity is caused by a high concentration of hydrogen ions. and an alkali close ...

Phosphoric Acid Titration | PDF | Titration | Chemistry - Scribd Phosphoric Acid, H3PO4 (pK1= 2.16, pK2 = 7.16, pK3=12.3). Phosphoric acid can be titrated as a monobasic acid: H3PO4 + NaOH → NaH2PO4 + H2O. The pH of a solution of resulting dihydrogen phosphate is: The change of the pH near equivalence point is not very pronounced.

Titration Of Phosphoric Acid With Naoh - globaldatabase.ecpat.org This article focuses on the titration of phosphoric acid (H₃PO₄), a weak triprotic acid, with sodium hydroxide (NaOH), a strong base. Understanding this specific titration is fundamental to grasping acid-base chemistry and its applications in various fields, from environmental monitoring to …

LABORATORY EXPERIMENT 4 - Buffalo State College Phosphoric Acid, H 3 PO 4 (pK 1 = 2.16, pK 2 = 7.16, pK 3 =12.3). Phosphoric acid can be titrated as a monobasic acid: H 3 PO 4 + NaOH → NaH 2 PO 4 + H 2 O The pH of a solution of resulting dihydrogen phosphate is: The change of the pH near equivalence point is not very pronounced. Phosphoric acid can also be titrated as a dibasic acid, with ...

Aim - Potentiometric titration of phosphoric acid solution ... - Studocu The aim of a potentiometric titration of phosphoric acid solution against sodium hydroxide is to determine the concentration of phosphoric acid in a solution by

Investigating an Acid Mixture - Vernier Understanding the behavior of the acids as they dissociate is a key component to evaluating the results of the titration. Titrate a mixture of HCl and H3PO4 with standard NaOH solution. Calculate the molar concentration of each acid in the mixture. Calculate the Ka2 (or pKa2) for the weak acid. 1. Obtain and wear goggles. 2.

Instrumental Analysis - NaOH, pH, and Titration of Phosphoric Acid In this lab, you will first make your own NaOH solution, standardize it using conductivity, thus getting a molarity to 4 significant figures, then you'll use that standardized base solution to titrate a solution of phosphoric acid.

Purity determination of phosphoric acid | Autotitrator COM-A19 21 Jun 2023 · The purity of phosphoric acid is determined by the titration to the second inflection point in this measurement. H₃PO₄ + NaOH → NaH₂PO₄ + H₂O ・・・(1)

Titration Of Phosphoric Acid With Naoh